1. Field of the Art
This invention is in the field of power measurement using dynamometers and, more specifically, inertial dynamometers. With inertial dynamometers the power being generated by a prime mover is measured by adding the results of the use of the power rather than by absorption of the power and measurement of the energy absorbed. The invention also is in the field of sensors, electronics and display means used in the implementation of dynamometer systems.
2. Prior Art
There is a large amount of prior art in these fields. Only the art considered to be directly pertinent and closest to the subject invention is cited and discussed, along with the following discussion of basics.
The basic methods for the measurement of horsepower have remained unchanged for over a century. They, for the most part, have been dedicated to the measurement of horsepower under stationary conditions. Although there have been methods by which horsepower could be determined under dynamic conditions, their use has generally been encumbered by various shortcomings. It became apparent in recent years that there was a need for an improved method and an apparatus that would both measure the horsepower of the prime mover and determine the drag characteristics of a moving vehicle. Attempts have been made at satisfying the above needs, but these attempts have fallen short of providing a new and complete method and apparatus for the measurement of prime mover horsepower and related dynamic vehicular characteristics of a moving vehicle. The methods and apparatuses of the prior art are discussed below, citing the advantages and disadvantages of each.
The horsepower of a prime mover, i/e: an engine or motor, has usually been determined with an absorption dynamometer. This class of dynamometer uses an absorption unit to dissipate horsepower in the form of heat and is generally restricted to prime movers with a rotary type of output. During the process of testing, the torque (lb/ft) and rpm are measured and Horsepower is then derived via mathematical procedure. With this method: EQU Horsepower=(torque.times.rpm)/5252 (a)
There are two basic styles of absorption dynamometers: the engine dynamometer, which takes horsepower directly from the prime mover, and the chassis dynamometer, which takes horsepower from the drive wheels of the vehicle. The above absorption dynamometers are noted for their high accuracy of measurement but they also have several drawbacks, as follows:
They are limited to stationary operation as they are not capable of measuring the horsepower of the prime mover in a moving vehicle.
The horsepower values are valid only at the time of testing and the procedure must be repeated if future tests are required.
The engine dynamometer often requires the removal of the prime mover from the vehicle.
They are frequently abusive to the prime mover as they often require runs at peak horsepower for sustained periods in order to obtain readings.
They do not test the prime mover under real world conditions. i/e: Driving the vehicle on the road under true environmental conditions.
Cost is also a considerable factor when testing with absorption dynamometers since basic unit costs start at many thousands of dollars. Additionally, they often require support systems such as a test cell, a control console, a large water supply, an exhaust system, a large air circulation system, and other items. The use of the absorption dynamometer is generally limited to the automotive professional or the serious auto racer because of this expense factor.
Another method by which the horsepower of the prime mover may be determined is to employ a torque sensor means in the vehicle itself. This sensor can be of the type that is installed in series with the drive train of the vehicle or it may take on the form of a sensor that detects the rotation of the prime mover against its mount. The torque and rpm are measured and the horsepower is calculated in the same manner as that of the absorption dynamometer (a). This method does not require support systems and has the advantage of being able to determine prime mover horsepower while driving the vehicle on the road under true environmental conditions. The disadvantage is that a torque sensor with any degree of accuracy is generally very expensive and difficult to implement.
A significant shortcoming of both the absorption dynamometer method and the in-vehicle torque sensor method is the fact that they determine the output horsepower of the prime mover only. They are not capable of measuring the horsepower dissipated by the vehicle due to such dynamic vehicular characteristics as:
Aerodynamic drag due to air resistance.
Frictional drag due to tire deformation and the moving parts of the vehicle.
Viscous drag due to the working of the tires and the lubricants of the vehicle.
The amount of horsepower lost to drag can become quite large with some vehicles, even at relatively low speeds. High amounts of drag due to friction may indicate a vehicular malfunction. Excessive drag causes a proportionate loss of fuel economy. Aerodynamic drag becomes a major factor limiting the top speed of a racing vehicle. Because of these facts, the knowledge of the amount of horsepower lost to drag is of great importance to all facets of the automotive and transportation industry.
The basic laws of physics suggest that there is yet another method of determining the horsepower of the prime mover or the drag characteristics of a moving vehicle. From these laws, it can be shown that the horsepower required to accelerate a vehicle may be defined by the equation: EQU Horsepower=mavK (b)
where:
m=The total mass (w/g) of the vehicle PA1 a=The instantaneous acceleration of the vehicle PA1 v=The instantaneous velocity of the vehicle PA1 K=A constant determined by the definition of horsepower PA1 a'=The absolute value of the instantaneous acceleration of the vehicle while coasting in neutral. PA1 v=The instantaneous velocity of the vehicle PA1 a=The signed value of the instantaneous acceleration of the vehicle PA1 a'=The absolute value of the instantaneous acceleration of the vehicle while coasting in neutral PA1 m=A constant determined by the total mass of the vehicle PA1 K=A constant determined by the definition of horsepower PA1 K'=A constant determined by the drive ratio of the vehicle PA1 K"=A constant determined by the desired sensitivity of instrument
In the above equation (b), the vehicle must be accelerating to obtain an indication of horsepower. The vehicle is also assumed to be perfect, with zero loss of horsepower due to vehicular drag. If a real world vehicle were to travel at a constant speed, the acceleration being neither positive or negative, the formula (b) would yield the incorrect (due to vehicular drag) answer that zero horsepower is required to maintain speed. Under accelerating conditions, the indication would be that of "Net" horsepower; i/e: the horsepower in excess of all other horsepower dissipated by vehicular drag. Therefore the above method and equation (b) may not be used directly to determine the "Gross" horsepower of the prime mover of a vehicle. Under real world conditions the equation (b) must be redefined to state: EQU Net Horsepower=mavK (c)
By again rewriting the equation (b), a formula is produced that allows for the determination of the actual horsepower lost due to vehicular drag, thus: EQU Drag Horsepower=ma'vK (d)
where:
The Gross horsepower delivered by the prime mover to the drive train in a moving vehicle is the algebraic sum of the net horsepower and the Drag horsepower. Therefore, by combining the above equations (c) and (d), the Gross horsepower of the prime mover may be defined by the equation, EQU Gross Horsepower=m(a+a')vK (e)
The preceding methods and equations work well in principle but they have not received wide spread acceptance in the past because of difficulties in the simultaneous measurement and multiplication of the instantaneous values of acceleration and velocity.
Additionally, the concept of continuous Gross horsepower measurement has been and is further complicated by the need for a means of determining the value of coasting acceleration at any given velocity while simultaneously adding this coasting acceleration value into the Gross horsepower equation (e) during the measurement process.
With the maturation of the semiconductor industry, it has been recognized that the problems of simultaneous measurement and multiplication could be overcome with solid-state electronic techniques. Apparatuses have been developed which include a means of determining acceleration, a means of determining velocity, a means whereby acceleration and velocity could be multiplied by each other and an indicating means. The operation of these instruments depends on the previously described laws of physics and relies exclusively on the calculation process expressed by the basic equation (b), Horsepower=mavK. The vehicular mass [m] and the constant [K] are generally considered as fixed values and are factored into the overall system gain of these apparatuses. Although these instruments are conceivably capable of measuring Net horsepower, Drag horsepower, Net torque, acceleration and velocity, they often suffer from one or more of the following imperfections:
The apparatus is capable of indicating horsepower under conditions of acceleration only.
The multiplier means is not fully bilateral nor truly linear, since a bipolar transistor was employed in this portion of the circuitry. This type of transistor conducts poorly in the reverse direction and is subject to an offset voltage because of its saturation characteristics. As a result, the accuracy of the instrument is degraded while measuring Drag horsepower and low levels of Net or Drag horsepower.
The apparatus will not accurately measure horsepower or acceleration on anything other than an absolutely level roadway surface since an inertial type accelerometer is not used to determine acceleration. Instead, the acceleration is derived from the velocity of the vehicle and the apparatus is not sensitive to the actual force propelling the vehicle.
The techniques employed to compensate for changes in angle of attack of the accelerometer do not provide accurate error correction for all grades of roadway. (Note: Angle of attack refers to the acute angle between the sensitive axis of the accelerometer and a line parallel to the roadway surface.)
The indicator does not read in actual horsepower units as a convenient means is not provided to calibrate the instrument with respect to vehicle mass.
None of the prior art apparatuses, including prior developmental units of the subject invention, were capable of implementing the calculation process expressed by the equation (e): Gross horsepower=m(a+a')vK. Therefore the above attempts by those skilled in the art were not successful in producing a method or apparatus that would conveniently or continuously measure the Gross horsepower produced by the prime mover and delivered to the drive train in a moving vehicle.
The most pertinent known prior art comprises six U.S. patents, a magazine article and several developments made by the inventor in the process of conceiving the subject invention. The U.S. patents are:
U.S. Pat. No. 2,318,645, May 11, 1943, "Horsepower Meter", C. D. Waldron PA0 U.S. Pat. No. 3,494,204, Feb. 10, 1970, "Accelerometer Producing A Linear Electrical Output", H. S. Whitehead PA0 U.S. Pat. No. 3,581,561, June 1, 1971, "Engine Acceleration Horsepower-Metering System", Tomoshek et al PA0 U.S. Pat. No. 3,693,426, Sept. 26, 1972, "Portable Useful Horsepower Measuring Instrument", D. R. Little PA0 U.S. Pat. No. 3,729,989, May 1, 1973, "Horsepower and Torque Measuring Instrument", D. R. Little PA0 U.S. Pat. No. 3,583,002, Dec. 10, 1974, "Vehicular Performance Analyzer", G. H. Peck PA0 Non-Servo Linear Accelerometer; H. G. Middleton; Dec. 10, 1962 PA0 Applied Ground Horsepower Formula; H. Middleton; Oct. 21, 1965 PA0 Thrustometer; H. G. Middleton; Feb. 9, 1967 PA0 Inertial Dynamometer; H. G. Middleton; June 29, 1980 PA0 Gain v/s Freq; H. G. Middleton; July 15, 1980 PA0 Inertial Dynamometer; H. G. Middleton; July 21, 1980 PA0 Inertial Dynamometer; Riv. 8-7; H. G. Middleton; Aug. 7, 1980 PA0 Inertial Dynamometer; H. G. Middleton; Oct. 10, 1982 PA0 Gross prime mover horsepower PA0 Net prime mover horsepower PA0 Gross prime mover torque PA0 Net prime mover torque PA0 Gross acceleration (+ or -) PA0 Net acceleration (+ or -) PA0 Vehicular velocity PA0 Gross force propelling the vehicle PA0 Net force propelling the vehicle PA0 Horsepower dissipated by aerodynamic drag PA0 Horsepower dissipated by frictional drag (optional) PA0 Horsepower dissipated by viscous drag (optional) PA0 Total horsepower dissipated by the combined effects of aerodynamic, frictional and viscous drag PA0 Frictional horsepower of the prime mover or drive train components PA0 Horsepower dissipated by the brakes of the vehicle PA0 Aerodynamic resistance to vehicular motion PA0 Frictional resistance to vehicular motion (optional) PA0 Viscous resistance to vehicular motion (optional) PA0 Resistance to vehicular motion due to braking of the vehicle PA0 The coefficients of aerodynamic, frictional or viscous drag (optional)
The magazine article, published in Hot Rod Magazine in 1974, was titled Driveable Dyno.
The prior art produced by the subject inventor comprises sketches, notes, equations, etc., recorded on drawings and in inventions, concepts, notebooks, workbooks, and laboratory notebooks. The following is a list of the concepts most pertinent to the eventual conception of the subject invention.
In view of the cited shortcomings of and difficulties with the prior art, it is specifically the primary object of this invention to provide a small, lightweight, inexpensive, convenient to use, accurate, multimode instrument that will determine, on any roadway grade, the performance characteristics of the prime mover in a moving vehicle and the dynamic vehicular characteristics of said moving vehicle.
Another object of this invention is to provide improvements over prior methods and apparatuses for the measurement of prime mover horsepower and torque in a moving vehicle and the drag characteristics of a moving vehicle.
Still another object of this invention is to provide a method and apparatus, having a convenient means for the calibration of the instrument with respect to vehicle mass therein, for the determination of the prime mover performance characteristics in a moving vehicle and the dynamic vehicular characteristics of said moving vehicle.
And still another object of this invention is to provide a method and apparatus whereby, at any given velocity, the value of the coasting acceleration of the moving vehicle may be determined and retained by circuitry within said apparatus. This retained value of coasting acceleration may then be used to compute the value of coasting acceleration at any given velocity as part of the calculation process during the determination of any vehicular parameter requiring the knowledge of the value of coasting acceleration during the measurement process.
Yet another object of this invention is to provide a method and an apparatus whereby the following vehicular parameters may be instantaneously measured and indicated while operating in a moving vehicle:
Total resistance to vehicular motion due to the combined effects of aerodynamic, frictional and viscous drag
And yet another object of this invention is to provide a method and apparatus whereby the lateral acceleration and lateral force may be determined during turning maneuvers.
A further object of this invention is to provide a method and apparatus whereby the degree of incline of a roadway grade may be determined.
Yet a further object of this invention is to provide a method and apparatus whereby the prime mover horsepower and the dynamic vehicular characteristics of a moving vehicle may be permanently recorded.
And yet a further object of this invention is to provide an improved method whereby compensation may be made for changes in the angle of attack of the acceleration sensing device (accelerometer).
A significant object of this invention is to provide a method and apparatus whereby the instrument may act as a driving aid for the improvement of fuel economy and the early detection of vehicular malfunction.
A meaningful object of this invention is to provide a method and apparatus for the determination of the performance characteristics of the prime mover and drag characteristics of any type of moving conveyance, in or on any type of transporting medium.
These and other objects of the above described invention will become obvious to those skilled in the art from the following detailed description of the preferred embodiment of this invention in reference to the accompanying drawings.
In the attainment of the foregoing objects, the preferred embodiment of this invention "the Inertial Dynamometer" is a multimode instrument intended for the real-time determination of the prime mover performance characteristics in a moving vehicle and the dynamic vehicular characteristics of the moving vehicle. Specific equations, derived from the laws of physics, are utilized by the apparatus of this invention during the determination of these characteristics, thus EQU Vehicular velocity=vK" (f) EQU Net vehicular acceleration (+ or -)=aK" (g) EQU SIN .theta. incline of roadway=aK" (g) EQU Lateral acceleration=aK" (g) EQU Gross vehicular acceleration (+ or -)=(a+a')K" (h) EQU Net force propelling the vehicle=maK" (i) EQU Lateral force=maK" (i) EQU Resistance to vehicular motion=maK" (i) EQU Gross force propelling the vehicle=m(a+a')K" (j) EQU Net prime mover torque=maK" (k) EQU Gross prime mover torque=m(a+a')K' (l) EQU Net prime mover horsepower=mavK (m) EQU Horsepower dissipated by vehicular drag=mavK (m) EQU Gross prime mover horsepower=m(a+a')vK (e) EQU Prime mover frictional horsepower=m(a+a')vK (e)
where:
The above equations (e thru m) are indicative of the modes of operation of the instrument and, as will be described, the apparatus of this invention measures, multiplies, adds and subtracts the variables a, a', v with the appropriate constants m, K, K', K" to resolve the individual equation for each mode of operation.
The subject invention, being a multimode apparatus and method for the measurement of the prime mover horsepower and the dynamic vehicular characteristics of a moving vehicle, retains the advantages of the previously discussed prior art and is not encumbered by the delineated disadvantages. The apparatus of this invention is called an "Inertial Dynamometer", since it utilizes an inertial accelerometer and relies on the inertia of the vehicle during the measurement process. As with the prior art, this instrument depends on the laws of physics to determine horsepower. Unlike the prior art, however, it employs the calculation process expressed by the equation (e): Gross horsepower=m(a+a')vK. The apparatus of this invention is similar to that of the prior art only in that it includes an acceleration determining means, a velocity determining means, a multiplier means and an indicating means. The acceleration and velocity determining means and the multiplier means of this invention provide substantial improvements over the prior art. The indicating means is that of any prior art. The apparatus also includes: a switch means whereby each mode of operation may be selected; a means whereby the mass of the vehicle may be factored into the calibration of the apparatus; a means whereby the output of the apparatus may be calibrated for all modes of operation; a means whereby the velocity determining means may be calibrated for any of various vehicles or types of velocity sensors; a means whereby the value of the coasting accelerator may be determined at any given velocity while simultaneously adding this value into the calculation process of the apparatus, and a means whereby effective compensation may be made for changes in angle of attack. In addition to horsepower, this apparatus is capable of measuring and indicating acceleration, force, resistance, torque, and velocity in a moving vehicle. With the vehicle at rest, the instrument may be used as an inclinometer to determine the roadway grade. If the accelerometer is positioned with the sensitive axis 90 degrees to the direction of travel, the lateral acceleration and force may be determined. With the addition of optional circuitry to the basic apparatus, the coefficients of friction, viscous, and aerodynamic drag may also be determined.